This invention relates to tube fittings of the deformable sleeve type and more particularly to a high pressure face seal type fitting in which the sleeve combines the mechanical grip of bite edges with the sealing efficiency of an elastomeric seal.
High pressure fittings of this type have been devised in the past with varying degrees of success. For example, in U.S. Pat. No. 4,529,231 there is shown a flat face tube connector having a face seal between the connector sleeve and the body to be sealed. In this fitting a plurality of radially projecting annular serrations are adapted to be compressed into fluid sealing engagement with the periphery of a tube and to supply the mechanical grip thereon as well. An elastomeric seal is described in this type of fitting for backup purposes but it is suggested that the seal is not necessary since a metal to metal seal is achieved at the gripping serrations. As seen in FIG. 1 of this patent, the elastomeric seal is urged under fluid pressure to the narrow end of a recess in the sleeve and cooperates with the embedded gripping serrations to prevent fluid leakage. It has been determined that this type of fitting does not provide a reliable fluid seal since the elastomeric seal does not consistently move to the narrow end of the internal recess and since the gripping serrations do not provide a reliable fluid seal in and of themselves as suggested in the disclosure.
Another form of prior art fitting which combines mechanical grip means and an elastomeric seal is shown in U.S. Pat. No. 2,466,527. In this design of fitting, a cutting edge at the rearward end of the sleeve is forced into biting engagement with the tube to provide a mechanical grip while an elastomeric seal is trapped in a recess at the forward end of the sleeve between the body member to be sealed and the inserted tube. A stop device is also shown in this design of fitting for controlling the axial interengagement between the nut and body member and thus the penetration of the cutting edge of the sleeve. However, this design of fitting is not particularly suited for high pressure applications since the rearward wall of the recess entrapping the elastomeric seal is sized for a free fit of the tubing therein leaving a gap through which the seal can extrude at high pressure levels.
A variation of this type of fitting is shown in U.S. Pat. No. 3,687,494. In this design of fitting, the forward cutting edge of the sleeve is forced into the periphery of the tube surface by a conical camming member while the rear end of the sleeve includes a recess closely conforming to the configuration of the entrapped elastomeric seal. This recess becomes deformed to a more open condition as the seal is compressed upon threaded engagement of the nut. Again, this type of fitting is not especially suited for high fluid pressure levels as little attention is directed to closure of the rear end of the recess of the sleeve, thereby allowing potential extrusion of the seal therethrough.
A similar form of fitting is shown in U.S. Pat. No. 3,025,084 which again includes the combination of the biting edge of a deformable sleeve member, and an entrapped elastomeric seal. This fitting also describes deformation of the annular recess containing the elastomeric seal in forcing the seal against the outer periphery of the tube. However, again, space must be provided between the rear end of the sleeve and the externally threaded nut to allow clearance for insertion of the tube therein, and this provides a path for extrusion of the elastomeric seal.
One form of prior art fitting which separates portions of a sleeve by a deformable bridge section is shown in U.S. Pat. No. 2,693,374. In this design of fitting, a face seal is effected at the forward end of the sleeve while a gripping edge is forced into the tube surface by means of a camming conical surface in the nut. An intermediate bridge section is deformed into engagement with the periphery of the tube and serves to confine the ridge formed by the cutting edge to provide a secure mechanical grip upon the tube combined with a fluid seal at that location. This type of fitting does not employ elastomeric seals at either the face seal location or within the recess of the sleeve at the bridge location.